SHADE_Y3/SHADE_Engine/src/Resource/Handle.h

#pragma once

#include <stdexcept>
#include <limits>

namespace SHADE
{
    /*---------------------------------------------------------------------------------*/
    /* Forward Declarations                                                            */
    /*---------------------------------------------------------------------------------*/
    template<typename T>
    class ResourceLibrary;
    
    /*---------------------------------------------------------------------------------*/
    /* Type Definitions                                                                */
    /*---------------------------------------------------------------------------------*/
    /// <summary>
    /// Exception thrown when an invalid Handle was dereferenced.
    /// </summary>
    class InvalidHandleException : std::runtime_error
    {
        /*-----------------------------------------------------------------------------*/
        /* Constructors                                                                */
        /*-----------------------------------------------------------------------------*/
        using std::runtime_error::runtime_error;
    };

    /// <summary>
    /// Base implementation of the Handle that is not templated to allow for holding
    /// generic non-type-specific Handles.
    /// </summary>
    class HandleBase
    {
      public:
        /*-----------------------------------------------------------------------------*/
        /* Type Definitions                                                            */
        /*-----------------------------------------------------------------------------*/
        /// <summary>
        /// Native ID type of a handle
        /// </summary>
        union Id
        {
            /*-------------------------------------------------------------------------*/
            /* Data                                                                    */
            /*-------------------------------------------------------------------------*/
            uint64_t Raw = std::numeric_limits<uint64_t>::max();
            struct
            {
                uint32_t Index;
                uint32_t Version;
            } Data;
        };

        /*-----------------------------------------------------------------------------*/
        /* Usage Functions                                                             */
        /*-----------------------------------------------------------------------------*/
        inline Id GetId() const;

        /*-----------------------------------------------------------------------------*/
        /* Overloaded Operators                                                        */
        /*-----------------------------------------------------------------------------*/
        /// <summary>
        /// Converts to true if this is a valid Handle.
        /// </summary>
        inline operator bool() const;

      protected:
        /*-----------------------------------------------------------------------------*/
        /* Constants                                                                   */
        /*-----------------------------------------------------------------------------*/
        static constexpr Id INVALID_ID {};

        /*-----------------------------------------------------------------------------*/
        /* Data Members                                                                */
        /*-----------------------------------------------------------------------------*/
        Id id = INVALID_ID;
    };

    /// <summary>
    /// Generic implementation of a Handle object 
    /// </summary>
    /// <typeparam name="T">Type of the handle.</typeparam>
    template<typename T>
    class Handle : public HandleBase
    {
      public:
        /*-----------------------------------------------------------------------------*/
        /* Constructors                                                                */
        /*-----------------------------------------------------------------------------*/
        Handle() = default;
        ~Handle() = default;
        
        /*-----------------------------------------------------------------------------*/
        /* Usage Functions                                                             */
        /*-----------------------------------------------------------------------------*/
        /// <summary>
        /// Deallocates the object pointed to by this function.
        /// </summary>
        void Free();

        /*-----------------------------------------------------------------------------*/
        /* Overloaded Operators                                                        */
        /*-----------------------------------------------------------------------------*/
        /// <summary>
        /// Returns the underlying object pointed to by the Handle.
        /// </summary>
        /// <exception cref="InvalidHandleException">
        /// Thrown when this is an Invalid Handle.
        /// </exception>
        /// <returns>Reference to the object pointed to by this Handle.</returns>
        T& operator*();
        /// <summary>
        /// Returns the underlying object pointed to by the Handle as read-only.
        /// </summary>
        /// <exception cref="InvalidHandleException">
        /// Thrown when this is an Invalid Handle.
        /// </exception>
        /// <returns>Const reference to the object pointed to by this Handle.</returns>
        const T& operator*() const;
        /// <summary>
        /// Provides access to members of the underlying object pointed to by the Handle.
        /// </summary>
        /// <exception cref="InvalidHandleException">
        /// Thrown when this is an Invalid Handle.
        /// </exception>
        /// <returns>Pointer to the object pointed to by this Handle.</returns>
        T* operator->();
        /// <summary>
        /// Provides read-only access to members of the underlying object pointed to by
        /// the Handle.
        /// </summary>
        /// <exception cref="InvalidHandleException">
        /// Thrown when this is an Invalid Handle.
        /// </exception>
        /// <returns>Const pointer to the object pointed to by this Handle.</returns>
        const T* operator->() const;

      protected:
        /*-----------------------------------------------------------------------------*/
        /* Data Members                                                                */
        /*-----------------------------------------------------------------------------*/
        ResourceLibrary<T>* library = nullptr;
        
        /*-----------------------------------------------------------------------------*/
        /* Friend Declarations                                                         */
        /*-----------------------------------------------------------------------------*/
        friend class ResourceLibrary<T>;
    };    

    /// <summary>
    /// Interface that needs to be implemented by classes that want to store a Handle to
    /// themselves after construction by Resource Managers.
    /// </summary>
    template<typename T>
    class ISelfHandle
    {
      public:
        /*-----------------------------------------------------------------------------*/
        /* Constructors                                                                */
        /*-----------------------------------------------------------------------------*/
        ISelfHandle() = default;
        ISelfHandle(const ISelfHandle& rhs);
        ISelfHandle(ISelfHandle&& rhs);

        /*-----------------------------------------------------------------------------*/
        /* Overloaded Operators                                                        */
        /*-----------------------------------------------------------------------------*/
        ISelfHandle& operator=(const ISelfHandle& rhs);
        ISelfHandle& operator=(ISelfHandle&& rhs);

        /*-----------------------------------------------------------------------------*/
        /* Usage Functions                                                             */
        /*-----------------------------------------------------------------------------*/
        /// <summary>
        /// Retrieves the Handle of this object.
        /// </summary>
        /// <returns>Handle to this object.</returns>
        Handle<T> GetHandle() const;
        /// <summary>
        /// Used to set the Handle for this object. Should only be used by 
        /// ResourceLibrary.
        /// </summary>
        /// <param name="rscLib">Required to lock usage to ResourceLibrary only.</param>
        /// <param name="hdl">Handle to set.</param>
        void SetHandle(const ResourceLibrary<T>& rscLib, Handle<T> hdl);

      private:
        /*-----------------------------------------------------------------------------*/
        /* Data Members                                                                */
        /*-----------------------------------------------------------------------------*/
        Handle<T> handle;
    };

}

namespace std
{
    /*---------------------------------------------------------------------------------*/
    /* Type Definitions                                                                */
    /*---------------------------------------------------------------------------------*/
    /// <summary>
    /// std::hash template specialization for Handle<T>
    /// </summary>
    /// <typeparam name="T">Type for the Handle.</typeparam>
    template<typename T>
    struct hash<SHADE::Handle<T>>
    {
        std::size_t operator() (const SHADE::Handle<T>& hdl) const;
    };
    /// <summary>
    /// std::hash template specialization for std::pair<Handle<T1>, Handle<T2>>
    /// </summary>
    /// <typeparam name="T">Type for the first Handle.</typeparam>
    /// <typeparam name="T">Type for the second Handle.</typeparam>
    template<typename T1, typename T2>
    struct hash<std::pair<SHADE::Handle<T1>, SHADE::Handle<T2>>>
    {
        std::size_t operator() (std::pair<SHADE::Handle<T1>, SHADE::Handle<T2>> const& pair) const;
    };
}

#include "Handle.hpp"